On a Stromberg Carlson Radio Model 654. The interstage xfmr between first stage audio, tube #27 to the grid of the output tube #45 is open both sides,
What is the impedance of each side?
Chuck

:On a Stromberg Carlson Radio Model 654. The interstage xfmr between first stage audio, tube #27 to the grid of the output tube #45 is open both sides,
:What is the impedance of each side?
:Chuck

That is a difficult question. The load on the secondary is reflected back into the primary. For example, if you have a 1:1 turns ratio, and connect the secondary to a 10K load, the primary impedance will be 1K Ohms. You really need to know the turns ratio rather than the impedance of the transformer.
Lewis
:

The secondary winding load is only the grid of the 45 tube, which will be very high impedance- an open, for all practical purposes. The primary would be several thousand ohms to roughly match the plate impedance of the driving stage tube; the secondary is about the same, the transformer most likely being 1:1.

:The secondary winding load is only the grid of the 45 tube, which will be very high impedance- an open, for all practical purposes. The primary would be several thousand ohms to roughly match the plate impedance of the driving stage tube; the secondary is about the same, the transformer most likely being 1:1.
:

::The secondary winding load is only the grid of the 45 tube, which will be very high impedance- an open, for all practical purposes. The primary would be several thousand ohms to roughly match the plate impedance of the driving stage tube; the secondary is about the same, the transformer most likely being 1:1.
::
:I wound up putting two 500K resistors across the interstage xfmr(500k grid to gnd on the 45 output tube and 500k feeding the plate of the 27 tube and a 0.01 cap. It works perfect. Sound came right on, pleanty of volume
:

:::The secondary winding load is only the grid of the 45 tube, which will be very high impedance- an open, for all practical purposes. The primary would be several thousand ohms to roughly match the plate impedance of the driving stage tube; the secondary is about the same, the transformer most likely being 1:1.
:::
::I wound up putting two 500K resistors across the interstage xfmr(500k grid to gnd on the 45 output tube and 500k feeding the plate of the 27 tube and a 0.01 cap. It works perfect. Sound came right on, pleanty of volume
::
:
:
Great job. I don't know why they didn't do that in the ole days, any how. Congrats to you.
Lewis

Notionally, transformer coupling is more efficient power-wise than RC coupling, since the DC resistance of the transformer is much lower than that of a plate resistor, so much less power is wasted as heat in the resistor.

But practically speaking, this is a "don't care". ITs are nice when driving push-pull output tubes, since they eliminate the need for an inverter tube, but for AM broadcast reception they don't add much (if anything) fidelity-wise. Particularly when one considers the limitations of most of the loudspeakers of the day.

500K in the plate circuit seems high to me, but it's tough to argue with success.

:Notionally, transformer coupling is more efficient power-wise than RC coupling, since the DC resistance of the transformer is much lower than that of a plate resistor, so much less power is wasted as heat in the resistor.
:
:But practically speaking, this is a "don't care". ITs are nice when driving push-pull output tubes, since they eliminate the need for an inverter tube, but for AM broadcast reception they don't add much (if anything) fidelity-wise. Particularly when one considers the limitations of most of the loudspeakers of the day.
:
:500K in the plate circuit seems high to me, but it's tough to argue with success.

I did lower the plate circuit to 250k on the 27 tube.
It does seem high but works very well.
Chuck

:Notionally, transformer coupling is more efficient power-wise than RC coupling, since the DC resistance of the transformer is much lower than that of a plate resistor, so much less power is wasted as heat in the resistor.
:
:But practically speaking, this is a "don't care". ITs are nice when driving push-pull output tubes, since they eliminate the need for an inverter tube, but for AM broadcast reception they don't add much (if anything) fidelity-wise. Particularly when one considers the limitations of most of the loudspeakers of the day.
:
:500K in the plate circuit seems high to me, but it's tough to argue with success.

CV, I did some more playing around. I have the plate resistor down to 20k and the plate voltage is about where it belongs. I can get more volume.
Chuck

FWIW, the 27 tube is rated at a plate current of 5 mA at 250 V (typical B+ voltage for a transformer-operated set); so this would equate to a plate resistance of 50K ohms. Most sets I've seen operate with plate resistances in the 75-100K ohm range; the higher the resistance, the longer your 27 tube will last; the lower the resistance, the more output volume you will have (generally speaking, of course). There's a happy medium somewhere in the middle.

:FWIW, the 27 tube is rated at a plate current of 5 mA at 250 V (typical B+ voltage for a transformer-operated set); so this would equate to a plate resistance of 50K ohms. Most sets I've seen operate with plate resistances in the 75-100K ohm range; the higher the resistance, the longer your 27 tube will last; the lower the resistance, the more output volume you will have (generally speaking, of course). There's a happy medium somewhere in the middle.

Thanks Lewis and CV. I did change the #27 plate resistor to 50K. Works fine and plate voltage somewhat lower than on schematic. That is OK as plenty of volume and clear sound. Glad to increase the life of the 27 tube
Chuck